This application claims the priority benefit of Taiwan application serial no. 90113302 and 90113302A01, filed Jun. 1, 2001 and Aug. 29, 2001.
1. Field of Invention
This invention relates in general to a method of fabricating an emitter of a field emission display (FED). More particularly, this invention relates to a method of fabricating a carbon nano-tube (CNT) type emitter of a field emission display.
2. Description of the Related Art
The current flat panel display includes the conventional cathode ray tube (CRT), the thin-film transistor liquid crystal display (TFT-LCD), the plasma display panel (PDP) and the field emission display. As the field emission display has a short optical response time for switching operation of the pixel circuit that fabricates the image, a better quality of display is obtained. The field emission display further has the properties of small thickness (about 2-10 cm), light weight (smaller than about 0.2 kg), wide vision angle (slightly large than 80xc2x0), high brightness (about 150 Cd/cm2), flexible working temperature (about xe2x88x920xc2x0 C. to about 80xc2x0 C.), and low power consumption (slightly smaller than 1 Watt). Thus, field emission display is one of the techniques with the most potential in the flat panel display industry in 21st century.
The field emission display is basically formed of two substrates with spacers between. The top glass plate is coated with phosphors as an anode plate. A gate plate can discharge field emission array (FEA) of an electron beam. The field emitted electrons from the gate are accelerated by the positive potential between the anode plate and the gate plate to bombard the phosphors. The so-called catholuminescence is generated.
Most field emission arrays of conventional field emission displays belong to the tip emitter type formed of pixels with a matrix addressing function. Each pixel comprises hundreds of minute tips. The tip structure has a dimension of about 1 micron (the tip bottom) with a curvature smaller than about 0.1 micron. The material of the tip includes molybdenum, tungsten, platinum, or a semiconductor such as silicon or diamond, such as the molybdenum tip used by Charles Spindt in 1976. The tip structure provided by Charles Spindt has the drawback of difficulties in using evaporation equipment and peeling technique. For example, the electron beam provided by the evaporator may cause the tip structure to have various tilt angles. In addition, the equipment is too huge to control. The reproducibility is low and the cost is too high, causing a problem for mass production.
Another kind of field emission display includes a carbon nano-tube (CNT) emitter that can use the simple thick film process to reduce cost.
In FIG. 1, a schematic drawing of a carbon nano-tube type emitter of a conventional field emission array is shown. In the method of fabricating such conventional nano-tube type emitter, a silver electrode 102 is formed on a substrate using screen printing. A carbon nano-tube layer 104 is formed on the silver electrode 102 to complete the fabrication of the carbon nano-tube emitter. The method of forming the carbon nano-tube layer includes mixing the carbon nano-tube material with a conductive epoxy or using chemical vapor deposition (CVD) with acetylene, ethylene or methane/hydrogen as the reacting gas. The reacting gas is then decomposed to grow the carbon nano-tube 104 with the aid of a catalyst of iron/cobalt/nickel under a high temperature. Another method for forming the carbon nano-tube 104 includes mixing the carbon nano-tube material with silver paste, which is then coated on the substrate 100 using a screen printing technique. As the device requires a large electric field of 2 to 6 V/m to emit electrons, a very large electric field is applied between the cathode and anode. If the carbon nano-tube material on the silver paste is not adhesive enough, it will cause the carbon nano-tube material to peel off. After peeling off, the carbon nano-tube particles and the large electric field induce the high speed electrons to simultaneously bombard the phosphors at the anode. The phosphors are thus exfoliated, shortening the lifetime of the device.
In addition, in view of carbon nano-tube material source, the yield of the carbon nano-tube material obtained by electric arc discharge is low and the adhesion thereof is poor. The carbon nano-tube material obtained from thermal decomposition of chemical vapor deposition or plasma-enhanced chemical vapor deposition (PECVD) has a high purity. However, such carbon nano-tube material still has the problem of poor adhesion.
As the carbon nano-tube is a carbon material with a large surface area, a large amount of gas is absorbed. Such absorbed gas causes a great problem in the later vacuum packaging process. It also causes unwanted arc discharge to affect the performance of the display.
The invention provides a method of fabricating an emitter of a field emission display. By coating a mixture of a metal with a low melting point such as tin, zinc, or aluminum, and silver paste, or coating a silver layer first, followed by a chemical coating or electroplate technique to coat a metal layer, the adhesion of the carbon nano-tube material is effectively enhanced.
The invention further provides a method of fabricating an emitter of a field emission display that forms a metal layer to cover a surface of the carbon nano-tube, so that the large amount of gas absorbed by and released from the carbon nano-tube is prevented.
The method of fabricating the emitter of the field emission display in the invention further includes raising the temperature after forming the carbon nano-tube, so that the glass material in the electrode is softened. Through the softening effect of the glass material, the adhesion between the electrode and substrate and carbon nano-tube is improved.
In the method of fabricating an emitter of a field emission display provided by the invention, a mixture of metal and silver paste with glass material is screen printed on a substrate as a silver electrode. Alternatively, the metal and the silver paste with glass material can be coated on the substrate separately. The above metal includes tin, zinc, aluminum or a hard solder alloy with a low melting point such as aluminum/silicon alloy. A catalyst layer can be formed on the silver paste to improve the subsequent carbon nano-tube formation process. The carbon nano-tube is formed on the silver paste, and a metal layer is formed on the carbon nano-tube. The metal layer comprises a nickel layer or a copper layer and has the function of preventing the carbon nano-tube from absorbing gas.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.